At least once every five years or whenever an increase in population density indicates either a change in class location for a segment of an existing steel pipeline operating at a hoop stress that is more than 40 percent of SMYS or that the hoop stress corresponding to the established maximum allowable operating pressure for a segment of existing pipeline is not commensurate with the present class location, the operator shall immediately make a study to determine:
(a) the present class location for the segment involved;
(b) the design, construction, and testing procedures followed in the original construction, and a comparison of these procedures with those required for the present class location by the applicable provisions of this Part;
(c) the physical condition of the segment to the extent it can be ascertained from available records;
(d) the operating and maintenance history of the segment;
(e) the maximum actual operating pressure and the corresponding operating hoop stress, taking pressure gradient into account, for the segment of pipeline involved; and
(f) the actual area affected by the population density increase, and physical barriers or other factors which may limit further expansion of the more densely populated area.